The present invention relates to a multi-piece solid golf ball. More particularly, it relates to a multi-piece solid golf ball having soft and good shot feel and excellent flight performance when hit by a golfer who swings a golf club at low head speed.
In golf balls commercially selling, there are solid golf balls such as two-piece golf ball, three-piece golf ball and the like, and thread wound golf balls. Recently, the two-piece golf ball and three-piece golf ball, of which flight distance can be improved while maintaining soft and good shot feel at the time of hitting as good as the conventional thread wound golf ball, generally occupy the greater part of the golf ball market. Multi-piece golf balls such as three-piece golf ball have good shot feel while maintaining excellent flight performance, because they can vary hardness distribution and design of golf balls, when compared with the two-piece golf ball.
The multi-piece solid golf balls are obtained by inserting an intermediate layer between the core and the cover layer constituting the two-piece solid golf ball and have been described in Japanese Patent Kokai Publication Nos. 322948/1997, 313643/1997, 57067/1999, 114094/1999, 253578/1999, 70408/2000, 70409/2000, 70414/2000, 189541/2000, 225209/2000, 296187/2000, 300695/2000 and the like. In the golf balls, it has been attempted to compromise the balance of flight performance and shot feel at the time of hitting by adjusting a hardness, hardness distribution and the like of the core, intermediate layer and cover to proper ranges.
In the golf balls described in Japanese Patent Kokai Publication Nos. 322948/1997 and 300695/2000, since the intermediate layer is formed from rubber composition, the durability is poor.
In the golf balls described in Japanese Patent Kokai Publication Nos. 313643/1997 and 296187/2000, since the hardness of the intermediate layer is higher than that of the core, the deformation amount when hit at low head speed is small, and the shot feel is poor.
In the golf balls described in Japanese Patent Kokai Publication Nos. 114094/1999, 253578/1999, 70408/2000, 70409/2000 and 189541/2000, the hardness of the intermediate layer is lower than that of the core. However, in the golf ball described in Japanese Patent Kokai Publication No. 114094/1999, since the thickness of the cover having higher hardness than the intermediate layer is large, the deformation amount at the time of hitting is small, and the shot feel is poor. In the golf ball described in Japanese Patent Kokai Publication No. 253578/1999, since the intermediate layer is formed from polyurethane, the rebound characteristics are poor, which degrades the flight performance. In the golf balls described in Japanese Patent Kokai Publication Nos. 70408/2000 and 70409/2000, since the hardness of the intermediate layer is too low, the rebound characteristics are poor, which degrades the flight performance. In the golf ball described in Japanese Patent Kokai Publication No. 189541/2000, since the hardness difference between the surface and center of the core is too small, the deformation amount at the time of hitting is small, and the shot feel is poor.
A golf ball has many depressions called xe2x80x9cdimplesxe2x80x9d on the surface. The dimples have function to disturb airflow around the golf ball on the fly and to facilitate turbulent transition at boundary layer so as to give rise to turbulent separation, which is called xe2x80x9cdimple effectxe2x80x9d. In the golf ball having aerodynamically excellent dimples, the facilitation of turbulent transition sifts the separation point of air from the golf ball to backward and reduces a drag coefficient. In addition, the facilitation of turbulent transition increases a difference of the separation point between an upper side and a lower side of the golf ball, caused by backspin of the golf ball, and enhances lifting power applied on the golf ball. The flight performance of the golf ball is improved for the reason. The properties of dimples have been variously studied in order to improve the flight performance of the golf ball.
In the golf balls described in Japanese Patent Kokai Publication Nos. 57067/1999, 70414/2000 and 225209/2000 among the golf balls described above, it has been attempted to compromise the balance of flight performance and shot feel at the time of hitting by adjusting properties of dimples, and hardness and hardness distribution of the core, intermediate layer and cover to proper ranges. However, in the golf balls, a correlation between the cover hardness and properties of dimples is not optimized, and there has been no golf balls, of which the balance between flight performance and shot feel at the time of hitting is sufficiently accomplished.
In addition, a main object of the above golf balls has been to improve a structure of the golf ball or flight performance of the hit golf ball. Therefore, there has been no golf ball having excellent flight performance while maintaining good shot feel when hit by a golfer who swings a golf club at low head speed. It has been required to provide golf balls, of which the shot feel and the flight performance are improved still more.
A main object of the present invention is to provide a multi-piece solid golf ball having soft and good shot feel and excellent flight performance when hit by a golfer who swings a golf club at low head speed.
According to the present invention, the object described above has been accomplished by providing a multi-piece solid golf ball, of which an intermediate layer is placed between a core and a cover, and by adjusting hardness difference between surface hardness and center hardness of the core; a hardness of the intermediate layer; hardness difference between the surface hardness of the core and the hardness of the intermediate layer; a ratio of a thickness of the cover to that of the intermediate layer; and properties of dimples; to specified ranges, thereby providing a multi-piece solid golf ball having soft and good shot feel and excellent flight performance when hit by a golfer who swings a golf club at low head speed.